Amplifier power control circuit

Abstract

A sense transistor is placed in a current path between a reference voltage source and ground. The base terminal of the sense transistor is coupled to the base terminal of an amplifying transistor. Thus, current in the sense transistor corresponds to signal power output by the amplifying transistor. The sense current causes a sense voltage at the collector terminal of the sense transistor. This sense voltage is applied to one input of an error amplifier. The other error amplifier input receives a power control voltage. The error amplifier output is routed back to the base terminal of the amplifying transistor in a negative feedback loop, thereby keeping the power of the signal output by the amplifying transistor at a constant level. In some embodiments the error amplifier output is made independent of changes in the reference voltage. Multiple pairs of corresponding amplifying and sense transistors can be used.

Description

BACKGROUND1. Field of InventionEmbodiments relate to electronic amplifier output signal power detection and control, particularly for radio frequency (RF) signals output from one or more final stage amplifying transistors.2. Related ArtMany electronic circuit applications require that output power of an amplifier be detected and controlled to maintain a specified level. Such an output power level may be required to change with time. In a Global System for Mobile communications (GSM) cellular telephone handset, for example, the final stage radio frequency (RF) amplifier outputs a signal to the antenna, and the power level of this signal must be controlled to maintain one or more precise levels. Therefore, it is important to be able to determine amplifier output power level and to control that power level.The power of a signal output from a Class C or similar transistor amplifier with non-continuous conduction corresponds to the collector current. In such amplifiers, two or more trans...

AI Technical Summary

Benefits of technology

Embodiments of the power control circuit offer several advantages, especially if formed on the same integrated circuit chip as the amplifier. In addition to being independent of the reference voltage (e.g., a power supply voltage) supplied to the chip, the power control circuit takes up only a small area on the chip. Further, cost is minimal since the power control circuit may be simultaneously fabricated with the amplifier and any associated on-chip circuits. Further, no output power is lost since the sense signal is taken from the input side of the amplifier. Such advantages are useful in, for example, cellular telephone handsets.

Problems solved by technology

Such an output power level may be required to change with time.

A disadvantage of directional couplers, however, is that some coupling loss exists as the output signal is sampled.

In addition, directional couplers are typically large, a condition which prevents the coupler from being on the same integrated circuit as the amplifier.

Furthermore, adding an off-chip coupler to an electronic device increases the cost of the device.

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